Wie viel wiegt das Vakuum? Kempf, Achim; Jonsson, Robert; Pye, Jason ...
Physik in unserer Zeit,
11/2023, Letnik:
54, Številka:
6
Journal Article
ZusammenfassungDas Vakuum ist nicht völlig leer, denn die Heisenbergsche Unschärferelation erzwingt Vakuumfluktuationen. Deren Existenz ist über Messungen der Casimir‐Kraft belegt. Folglich muss auch ...Energie in den Vakuumfluktuationen stecken, die sich nach E = mc2 in Form von Gravitation bemerkbar machen sollte. Nach der Allgemeinen Relativitätstheorie müsste ihre Gravitation die Expansion des Universums beschleunigen. Allerdings wäre die Gravitationswirkung, die sich theoretisch aus der quantenmechanisch ermittelten Grundzustandsenergie des Vakuums ergibt, um etwa 120 Größenordnungen zu groß. Dieser Widerspruch ist eine der grundlegenden, ungeklärten Fragestellungen der Physik. Auf der Suche nach einer Antwort soll das Archimedes‐Experiment als extrem empfindliche Waage die Energiedichte des Vakuums bestimmen. Das Resultat soll Hinweise auf die Ursache des „Problems der kosmologischen Konstante“ liefern.
Covering all aspects of gravitation in a contemporary style, this advanced textbook is ideal for graduate students and researchers in all areas of theoretical physics. The 'Foundation' section ...develops the formalism in six chapters, and uses it in the next four chapters to discuss four key applications - spherical spacetimes, black holes, gravitational waves and cosmology. The six chapters in the 'Frontier' section describe cosmological perturbation theory, quantum fields in curved spacetime, and the Hamiltonian structure of general relativity, among several other advanced topics, some of which are covered in-depth for the first time in a textbook. The modular structure of the book allows different sections to be combined to suit a variety of courses. Over 200 exercises are included to test and develop the reader's understanding. There are also over 30 projects, which help readers make the transition from the book to their own original research.
We tested the gravitational 1/r2 law using a stationary torsion-balance detector and a rotating attractor containing test bodies with both 18-fold and 120-fold azimuthal symmetries that ...simultaneously tests the 1/r2 law at two different length scales. We took data at detector-attractor separations between 52 μm and 3.0 mm. Newtonian gravity gave an excellent fit to our data, limiting with 95% confidence any gravitational-strength Yukawa interactions to ranges < 38.6 μm.
Correction for 'UniChip enables long-term recirculating unidirectional perfusion with gravity-driven flow for microphysiological systems' by Ying I. Wang and Michael L. Shuler
, Lab Chip
, 2018,
18
, ...2563-2574.
A
bstract
Entanglement entropy obeys a ‘first law’, an exact quantum generalization of the ordinary first law of thermodynamics. In any CFT with a semiclassical holographic dual, this first law has ...an interpretation in the dual gravitational theory as a constraint on the spacetimes dual to CFT states. For small perturbations around the CFT vacuum state, we show that the set of such constraints for all ball-shaped spatial regions in the CFT is exactly equivalent to the requirement that the dual geometry satisfy the gravitational equations of motion, linearized about pure AdS. For theories with entanglement entropy computed by the Ryu-Takayanagi formula
S
=
/
(4
G
N
), we obtain the linearized Einstein equations. For theories in which the vacuum entanglement entropy for a ball is computed by more general Wald functionals, we obtain the linearized equations for the associated higher-curvature theories. Using the first law, we also derive the holographic dictionary for the stress tensor, given the holographic formula for entanglement entropy. This method provides a simple alternative to holographic renormalization for computing the stress tensor expectation value in arbitrary higher derivative gravitational theories.
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